My earlier U.S. Pat. Nos. 3,080,265 and 3,380,461 describe a system for cleaning a conduit--an underground pipe or even an open trench--of a waste-disposal or sewage system. A nozzle is mounted on the downstream end of a high-pressure conduit and has at least one backwardly open water-ejecting aperture. Water supplied under high pressure to this nozzle is therefore ejected backwardly to displace the nozzle along in a conduit to be cleaned, pulling its hose behind it. As it moves forward the nozzle loosens sludge deposits and the like inside the conduit, in particular on the conduit floor. Backward withdrawal of the nozzle, while still spraying, effectively scoops the loosened deposits up and allows them to be flushed away. Such a system is replaceable with mechanical scraping devices, as it allows the conduit to be cleaned with a relatively simple tool without running the risk of damaging the interior of the conduit.
The hose is normally held on a large reel above ground, and is unreeled as the nozzle head jets itself along the conduit being cleaned. Naturally this unreeling causes the cable to twist so that a torsion is frequently applied to the nozzle at the hose end. In a relatively simple system wherein the nozzle is perfectly symmetrical about its longitudinal axis, the resultant rotation of the nozzle is by no means disadvantageous, in fact it helps to force the nozzle through the conduit.
A self-righting nozzle such as described in my jointly filed copending application No. 059,120 must be rotated about its longitudinal axis during use. Instead this nozzle should remain in a predetermined orientation with respect to the vertical for most efficient functioning, as most of the water-ejecting apertures are arranged to be directed downwardly. This is also the case for the pipe-cleaning head described in my above-cited U.S. Pat. No. 3,380,461.
Accordingly it is known to provide a swivel coupling at the end of the hose immediately upstream of the pipe-cleaning nozzle. Such a swivel allows the hose to twist without rotating the nozzle.
Such arrangements employ extremely high pressures and flow volumes. In fact water pressures in excess of 60 atmospheres-gauge are usually employed. At the same time the nozzle and swivel are normally employed in extremely dirty conditions. As a result the hitherto used swivels have proven unsatisfactory. They have a short service life as a result of the extreme conditions they must operate under. After a relatively short time most of the known swivels leak and/or no longer swivel, so that they must be serviced or replaced.